This invention relates to abrasive tools.
There are a variety of abrasive tools available which use ultra-hard abrasives such as diamond and cubic boron nitride (CBN) as the abrasive. Such tools include grinding wheels and saws.
Grinding wheels comprise a hub, typically made of a material such as bakelite, phenol-aluminium or aluminium, and a working rim secured to the periphery of the hub. The working portion will typically comprise a mass of ultra-hard abrasive particles dispersed in a metal matrix, vitreous matrix or in a thermosetting resin such as a phenol formaldehyde, urea formaldehyde or melamine formaldehyde resin. The hub may take the form of a flat disc or a cup.
One type of known saw comprises a flat circular blank or disc having a working portion bonded to the periphery thereof. The working portion may comprise a plurality of individual segments or a continuous rim. The working portion comprises a mass of ultra-hard abrasive particles dispersed in a metal bonding matrix. An example of a suitable metal bonding matrix is cobalt/bronze.
Another type of saw is a wire saw which comprises a wire having a plurality of annular segments bonded or secured to the wire in spaced relationship.
The manufacture of grinding wheels using thermosetting resins is ponderous and slow, the materials have poor heat conductivity and it may be necessary to heat a powder mix of such a material for four hours or more in an oven to set it.
In the literature there are described polishing materials comprising a flexible or similar support having a layer of abrasive particles in a binder resin bonded to a surface thereof. One such polishing material is described in U.S. Pat. No. 4,927,432. This polishing pad material comprises a porous thermoplastic resin matrix reinforced with a fibrous network and optionally containing abrasive particles such as silicon carbide, cerium oxide, titanium dioxide or diamond. The material is used for polishing silicon wafers by chemical attack, the pores being necessary to accommodate the liquid chemical reagent. The porous nature of the thermoplastic resin matrix renders the pad unsuitable for grinding and sawing operations where abrasion and not chemical attack of a workpiece occurs.